My car just came back from the shop the other day for top end work, it was running like a bat out of hell for over 100 miles, drove it yesterday and it was losing power and the exhaust was getting quieter and quieter to now the point it's so quiet, I have flowmaster cat back exhaust. The car won't Rev past 2500 rpm now and will not go anywhere, there is a wicked rattling/popping noise coming from under the passenger side floor. It doesn't smell really bad. I jacked it up and tried banging the cat there is a definite piece moving around loosely towards the front of the cat. There is just no power, brand new plugs, wires and opti. I did clean the k&n air filter with k&n cleaner. The filter wasn't all the way on when it was running awesome, I tightened it back on and now it's too this point. So I don't know. I unplugged the o2 sensors and no check engine light. The CEL did come on yesterday when it died out on the highway but went away after a couple starts any ideas

 

Single cat or dual cat? You need to provide year of engine/PCM for an accurate respoense. Only way we even know it's an LT1 is mention of the Opti. Can you scan it to see what turned on the SES light?

 

Single cat, and 95 both engine and pcm both stock and no I don't have a scanner

 

Bump

 

Either you or an exhaust shop need to install a pressure gauge in one of the O2 sensor bungs, and check for excessive back pressure.

For a free download of an excelent scanning software, check out the Scan9495 sticky at the top of the "Computer Diagnostics...." forum.